Good News Buried in Climate Change Report

March 24, 2014

The IPCC buried evidence in its latest report that indicated good news about global warming, according to a new study from climate scientist Nic Lewis and science writer Marcel Crok.

The UN Intergovernmental Panel on Climate Change, or IPCC, released its Working Group I (WGI) report, Climate Change 2013: The Physical Science Basis, in September 2013. The report proclaimed a 95 percent certainty that humans were responsible for most global warming since 1950. However, Lewis and Crok (who were expert reviewers of the report) say the report hid certain findings related to climate sensitivity.

Climate sensitivity is simply the measure of the climate's response to increased greenhouse gases. Higher sensitivity means that continuing, or increased, greenhouse gas emissions will lead to more warning, whereas low sensitivity means that any future warming (and associated responses, such as sea level rise) will also be low.

The measure of climate sensitivity is important because it is used to determine the impact of increased greenhouse gas emissions.

For 30 years, IPCC assessments and those of others have been able to provide no more than an uncertain range for climate sensitivity.

The latest IPCC report had no best estimate for climate sensitivity, which it admitted in a single footnote in its Summary for Policymakers.

Recent studies indicate that climate sensitivity is between 1.5 degrees and 2 degrees Celsius, significantly lower than what earlier studies had indicated. However, climate models still use high climate sensitivities (2 degrees to 4.5 degrees Celsius) to project future climate change. Had the IPCC said that the best evidence is that sensitivity is only between 1.5 degrees and 2 degrees Celsius, it would have admitted that large swaths of the report are not in line with the most recent evidence. To deal with this, it just extended the range from 1.5 degrees to 4.5 degrees Celsius.

Since the last IPCC report in 2007, greenhouse gas concentrations have risen but global temperatures have not. At the same time, estimates of the efficacy of aerosols to cause cooling have been reduced. However, the climate models do not take this new evidence about aerosols into account.

Lewis and Crok criticize the IPCC's "climate model-oriented...process." Because of those constraints, the latest report did not satisfactorily assess climate sensitivity, one of the most important parts of the climate change debate.